Military jet aircraft crew members have been wearing an anti-G protection suit for many years to protect themselves against "gray out" or "black out" experienced when performing high speed, turning maneuvers in an aircraft. These turning maneuvers may be in the horizontal plane as when the aircraft is changing its heading, in the vertical plane as when the aircraft is pulling out of a dive, or in a combination of the horizontal and vertical planes. The anti-G suit is typically a trouser-like garment which includes individual sections zippered about the pilot's calves, thighs and abdomen to provide a snug fit thereabout. These individual sections contain inflatable bladders which are connected to an aircraft air supply system through a detachable hose which is integrally connected to the G suit. As the pilot experiences greater accelerative forces, pressurized air is continually admitted into the inflatable bladders to increase the pressure about the pilot's legs and abdomen to reduce the amount of blood draining into these areas. In conventional aircraft G suit systems, accelerometers in the aircraft sense the accelerating force which the aircraft and aircrew member are experiencing. These accelerometers transmit a signal, either mechanically or electrically, to a valve interposed within an air supply system, to control the inflation of the G suit bladders to a predetermined pressure in order to offset the effects of the aircraft's acceleration. The purpose of the G suit is to reduce the flow of blood from the pilot's torso into the legs and feet during aircraft maneuvers where large accelerative forces are experienced. As the accelerative forces increase, there is a tendency for additional blood to leave the head and upper torso resulting initially in "gray out" where the pilot's vision begins to "tunnel" and blur, and then sometimes to "black out" where the pilot loses vision entirely, and ultimately loses consciousness. The pressurized G suit increases tissue pressure in the abdomen and lower limbs thereby maintaining peripheral vascular resistance and reducing blood pooling in the lower extremities. In addition, the abdominal bladder supports the abdominal wall thereby reducing the distance in which the aircrew member's breathing diaphragm is displaced downward, and minimizing the increase in vertical distance between the heart and the brain which the accelerative forces promote.
The environment in which military jet aircraft are typically subjected to the greatest amount of accelerative forces is in combat or simulated combat situations, such as air combat maneuvering (ACM), where aircraft are attempting to maneuver behind one another in order to direct their weapons. A critical element for surival in an ACM environment is the maintenance of the pilot's vision, including peripheral vision, in order to maneuver relative to the opposing aircraft. A significant problem with conventional G suit protection systems is the time delay between G force onset and G suit pressurization, thereby reducing the amount of protection afforded to the aircrew member. Conventional systems may take up to five seconds to pressurize the G suit to the desired pressure. Centrifuge tests have shown that gray out can occur as soon as one and one-half seconds after G force onset, and unconsciousness within three seconds of G force onset. See, for example, J. Ernsting, Aviation Medicine--Physiology and Human Factors, TRI-MED (1978), p. 231.
Accelerative forces are normally described in relationship to one G, or in other words, the accelerative force a body experiences at the earth's surface when at rest. Accelerative forces exceeding one G are described in terms of a factorial number of G's. For example, an aircraft in a tight turn might experience six G's or more, which is an accelerative force of six times the normal force of gravity. The present generation of military jet aircraft, such as the F-16, using sophisticated airframe materials are designed to be flown in a service envelope of up to nine G's. This is a significant increase over the previous generation of military jet aircraft which had service G limitations of six or seven G's. It should be appreciated that increasing the G tolerance of the aircraft allows the pilot to turn the aircraft at a higher rate, as well as through a smaller turn radius, to aid in maneuvering to an advantageous position relative to other aircraft. The physiological effects of experiencing G forces may vary according to the size and general health of the aircrew member. Without G suit protection, "gray out" can occur as low as three or four G's, while "black out" can occur as low as five or six G's.
Many military jet aircraft have service ceilings above 40,000 feet and are equipped with oxygen administered to the aircrew member through an oxygen mask worn about the mouth and nose. Typically, the oxygen system is a demand type apparatus wherein the oxygen is inhaled and exhaled as the aircrew member's lungs expand and contract. However, as the aircraft cockpit reaches an altitude of 40,000 feet or more, the oxygen must be supplied to the lungs at a pressure exceeding that of the cockpit to prevent hypoxia. Typically, the aircraft will include a positive pressure breathing system which automatically supplies oxygen under pressure to the mask and into the aircrew member's lungs to ensure an adequate supply of oxygen is maintained therein.
It has been found that high altitude positive pressure breathing is aided by exerting pressure against the upper portion of the body, particularly around the chest and abdominal areas, because the pressure exerted assists the aircrew member in exhaling breath gases from the lungs against the positive pressure in the face mask. Therefore, an inflatable garment called a counterpressure garment is worn around the chest and back area so that during positive pressure breathing the counterpressure garmet is also inflated to the same pressure as in the mask. It is also desirable in a high altitude environment to pressurize the anti-G suit to a predetermined ratio of the positive pressure in the breathing mask; e.g. typically four times mask pressure.
It has also been found that G protection is enhanced by positive pressure breathing because the increase in breathing pressure causes an approximately equal increase in heart level blood pressure, thereby increasing the flow of blood to the brain. Therefore, it is sometimes desirable to initiate positive pressure breathing at some minimum G force level. When the predetermined level of G force is encountered, or when the pressure in the G suit reaches an equivalent value, a signal is transmitted to a breathing regulator to initiate positive pressure breathing to the face mask, which by means of a valving system automatically initiates inflation of the counter pressure garment.
In U.S. Pat. No. 4,336,590--Jacq, et al, there is disclosed a regulatory apparatus for pre-inflating an anti-G suit to a predetermined fixed level, e.g., ten millibars, when actuated by a signal caused by rapid movement of the aircraft's control stick. The regulatory apparatus also causes pre-inflation of the anti-G suit to a slight pressure when it is signaled that positive pressure breathing is occurring.
In U.S. Pat. No. 4,230,097--Beaussant, et al, there is disclosed a regulating apparatus for controlling the gas pressure in an anti-G suit, including means for pre-inflating the G suit to a predetermined pressure level as soon as the flight controls of the aircraft are placed in a position which will cause acceleration of the aircraft. Inflation of the G suit to the required pressure is a function of the acceleration experienced by the aircraft and is controlled by an acceleration responsive control valve.
In U.S. Pat. No. 4,243,024--Crosbie, et al, there is disclosed a regulating apparatus for inflating an anti-G suit based upon a measured acceleration and an angle defined by an intersection of the vertical axis of the aircraft with the thoracic axis of the pilot.
In U.S. Pat. No. 3,780,723--Van Patten, et al, there is disclosed a control system for an inflatable G suit based upon the acceleration which the aircraft experiences summed with the time rate of change of the aircraft acceleration.
In U.S. Pat. No. 4,219,039--Jaggars, there is disclosed a control system for pressurizing an aircrew anti-G suit over a variable rate inflation schedule.
In U.S. Pat. No. 3,158,149--Gray, there is disclosed a control system for an inflatable jacket worn by an aircraft aircrew member wherein an acceleration responsive metering valve controls the amount of pressurized air supplied to the jacket.
In U.S. Pat. No. 3,089,482--Gray, there is disclosed a closed volume suit, containing an incompressible liquid therein, to be worn by an aircrew member so that the aircrew member's body is submerged in the liquid to counterbalance the distortion of body tissues caused by accelerative forces.
In U.S. Pat. No. 4,039,039--Gottfried, there is disclosed trousers having inflatable chambers which are worn by a patient experiencing a health emergency to immobilize the body or to reduce or inhibit bleeding in the lower torso and legs.
In West German Pat. No. WO 82/01464, there is disclosed a safety suit for a motorcyclist wherein the safety suit has chambers which automatically inflate upon the rider's rapid ejection from the motorcycle.